Geochemical Survey in the 1:100000 Sehchangi sheet
The study area is located in the west of city Birjand, in the Southern Khorasan. Tertiary volcanic rocks form the central and western hills of the area. In the southwest, limestone occurs in the Ali-Qorban and Gursefid mountains. Large Quaternary plains with gravel sediments form the eastern and northwestern portion of the region. There are several salt flats in the region. The area has dried climate with less than 50 mm average annual precipitation.
1:100000 sheet of Sehchangi includes four 1:50000 sheets of Nughab-e Bala, Nalineh, Kuh-e Changenamakzar and Gharb-e Noghab. The filed survey was conducted on the base of topography, 1:100000 geology map and 1:250000 airborne geomagnetic map.
In this project, 362 stream sediment samples were collected with consideration of weight center of drainage basins that is controlled by lithology, stratigraphy and tectonics.
Five groups of experts were set out to the area to collect the samples. Each sample involves 100 to 200 grams of 80 mesh stream sediments that sieved, dried, packed and numbered. After analysis of samples and processing the obtained data, several primary anomalies were identified that should be checked by other methods. Heavy mineral sampling was selected as a tool for controlling the geochemical anomalies. About 100 heavy mineral samples were collected for this.
To model the geochemical anomalies in the Sehchangi sheet, we used these data, the stratigraphy, host rock of anomaly, the age of host rock, probable alterations in the zone, geochemical parageneses, ores and minerals in the heavy minerals samples, structure and texture, weathering products, and tectonic setting.
Among 15 identified anomalies in the area, five ones were modeled from which only three anomalies have required data for modeling. These models include:
1- Anomaly number I in the Kuh-e Changenamakzar 1:50000 sheet, near the southwest of Sehchangi mine. The anomaly correlated with epithermal vein, hot spring Au-Ag, Comstock epithermal vein and Cyprus-type massive sulfide deposits; respectively.
2- Anomaly number VI in the Nalineh sheet: it is located 5 km away from the northwest of Kalat-e Zeynab. This anomaly correlates with sandstone-hosted lead-zinc, layered barite, sedex, Cyprus-type massive sulfide and replacement polymetal deposits, respectively.
3- Anomaly number V: it is located in the Nalineh sheet, four Km away from northeast of Anjireh mountain, it correlates with Appalachia type deposit.